We examine the problem of control of high-performance drives and servos with permanent-magnet stepper motors. Control of electromechanical systems implies control and optimization of electromechanical transductions and energy conversion. Robust spatio-temporal control algorithms are designed to ensure high efficiency, high-precision microstepping and optimal performance. The system stability, robustness and control design are examined applying an admissibility concept. Nonlinear control guarantees optimal energy conversion in expanded operating envelopes. Our analytic designs are substantiated and verified. A proof-of-concept system is tested and characterized. The high electromagnetic torque and high-precision microstep angular positioning simplify kinematics, enables efficiency, ensures direct-drive capabilities, reduces complexity, etc. For four-phase permanent magnet stepper motors, one may ensure up to 256 microsteps within a 1.8 degrees full step. High efficiency and accurate 2.454 x 10(-4) rad positioning (25,600 microsteps per revolution) are achieved with high electromagnetic and holding torques. To guarantee high efficiency, optimality and enabled energy conversion capabilities, electromechanical energy conversion and high electromagnetic torque are achieved by applying soft balanced phase voltages. The ripple and friction torques are minimized. The fundamental findings, technology-centric design and experimental results are reported. (c) 2014 Elsevier Ltd. All rights reserved.